Method of and means for measuring dipole moments of gases or vapors



NG DIPOLE W. D. HERSHBERGER METHOD OF AND MEANS FOR MEASURI MOMENTS 0FGASES 0R VAPORS Filed July 26, 1946 DETECTOR MICRGIWE INVENTOR. GilliamD.Hers11berger M/C'ROWA VE RE CE V It A T TUR/VE Y 6A8 OUTLET lm ml mSWEAT GENEVA 70/? 6145 our; 5r

MICROWAVE sis/ML SOURCE SOURCE MICROWAVE Mopuufla/v Patented Oct. 3,1950 UNITED STATES PATENT OFFICE METHOD OF AND MEANS FOR MEASURINGDIPOLE MOMENTS OF GASES OR VA PORS William D. Hershberger, Princeton, N.J assignor to Radio Corporation of America, a corporation of DelawareApplication July 26, 1946, Serial No. 686,482

, thereof.

The instant invention comprises improvements upon and modifications ofthe systems and methods described and claimed in applicant's copendingapplication Serial No. 956,242, filed May 28, 1945, wherein analysis ofgas composition is provided by measurements of the microwave energyloss, variations of dielectric constant and the frequency of theirradiating microwaves as a function of the gas pressure. I

The instant invention also is an improvement upon the methods andsystems described and claimed in applicant's second copendingapplication Serial No. 596,244, filed May 28, 1945, which employmodulated microwaves for such gas analyses. In said latter applicationthe modulated microwaves have a frequency providing appreciablemicrowave absorption in at lea'st some components of the gaseousmixture. The gaseous mixture is irradiated by the modulated microwavesand is enclosed within a cavity resonator which is electrically resonantto the microwave carrier frequency and which is acoustically resonant tothe modulation component of the modulated microwaves. Due to varyingcharacteristics of different gases, the acoustic resonant frequency maybe made a function of the gas composition, as well as of gas pressure,temperature and rate-of-fiow in a continuous process.

Such gas analyses are extremely useful in monitoring chemicalmanufacturing processes as well as for indicating operatingcharacteristics, or for controlling the operation of such processes.Output potentials derived from a microwave detector may be applied tocontrol suitable devices such as pressure regulators, control valves,mixing jets, or controls for regulating the gas-flow characteristics ina continuous gas analysis system.

All such gas detection or analysis systems dependent upon microwave gasabsorption, or variations in dielectric constant, in a microwaveabsorptive gas require considerable microwaveabsorptive gas pressure inorder to provide reasonable measurement sensitivity. Heretofore, gasproduction processes frequently have required the taking of samples ofthe gases for chemical or spectroscopic analyses. Such analyses requireconsiderable time and also may require that the production process beinterrupted until the Claims. (Cl. 175-183) analysis is completed, thusnecessitating considerable delayand expense.

The instant methods and systems provide continuous analyses of anydesired portions of such production processes thereby permitting eithermechanical or automatic control of the production processes when the gascomponents vary between predetermined marginal limits. When complicatedgaseous mixtures are involved, such as in the manufacture of butadienein synthetic rubber production, there is always the possibility ofproduction of gases other than those desired. In accordance with theinstant invention, direct and simultaneous indications may be providedof the presence and relative amounts or proportions of all gases orvapors in the mixture having dipole moment characteristics.

The instant invention contemplates utilization of the rotation of theelectric fleld of microwave propagation through gases or vapors havingdipole moments as a combined function of the magnitude of the dipolemoment, the frequency of the microwave propagation, and the magnitude ofan applied electrostatic field through which the microwaves arepropagated. A first embodiment of the invention comprisesa pair ofwaveguides having perpendicularly disposed electrical axes, saidwaveguides being coupled together through a third wavepath disposedbetween the ends of said pair of waveguides. The microwaves propagatedthrough the third wavepath are subjected to an adjustable electrostaticfield which rotates the electric field of the propagated microwaves as acombined function of the dipole moment of gases or vapors introducedinto said wavepath, the frequency of said microwave propagation, andthefield strength of said adjustable electrostatic field.

In the absence of gases or vapors having dipole moments, there issubstantially zero coupling between the first two of saidperpendicularly disposed waveguides. Adjustment of the potentialproviding the adjustable electrostatic field in the third wavepaththerefore may selectively provide rotation of the electric field of thepropagated microwaves which thence may be detected in the second of saidpair of waveguides. The voltage range required for producing therequired electrostatic field in the third wavepath is a function of thefrequency of the microwaves; propagated through the system. If desired,a continuous gas or vapor flow may be provided through the thirdwavepath for continuous gas or vapor analysis.

A second embodiment of the invention comprises a pair of telescopingrectangular cavity resonators, operating in modes such that the electricfield of the first is perpendicular to the electric field of the secondin the volume common to both, and separated by parallel disposed wirescreens, or by slotted walls having perpendicularly disposed screenapertures. A microwave source may be coupled into one of said resonatorsby means of a coupling loop, or other known coupling device, and anoutput coupling element may be provided in the other of saidintersecting resonators. The gas or vapor to be analyzed should becirculated through both of the telescoped resonators. If desired, thegas may be confined to the common portion of the two resonators bygas-tight, microwave permeable windows disposedadiacent and parallel tothe screen elements. The two resonators should be electrically insulatedfrom one another at a point interme-.

diate the oppositely oriented, parallel disposed screens or slottedwalls. An adjustable unidirectional potential applied to the tworesonators provides an adjustable electrostatic field between theoppositely oriented screens. Adjustment of the electrostatic fieldmagnitude thereby provides selective adjustment of microwave couplingbetween the cavity resonators as a function of the microwave frequency,the dipole moments of the gases circulated through said resonators, andthe magnitude of the electrostatic field in the space intermediate thetwo screens. v

A third embodiment of the invention utilizes a pair of intersectingcavity resonators of the type described wherein the magnitude of theelectrostatic field established between the screens is varied by signalsderived from a modulation signal source. A microwave receiver coupled tothe second of said cavity resonators is connected to the verticaldeflection electrodes of a cathode ray oscilloscope or otheros'cillographic indicator. A timing wave generator synchronized with oractuated by the modulation signal source is connected to the horizontaldeflecting elements of the oscilloscope. The effective range of thesystem may be controlled by an adjustable unidirectional potentialsource connected between the insulated cavity resonators and byselection of a suitable microwave frequency for the microwave signalscoupled into the first of said resonators. If desired, the timingfrequency generator may provide a modified sawtooth waveform forexpanding a desired portion of the oscilloscope scale. Directindications are provided of the relative dipole moments and relativeproportions of all gaseous or vapor components of the gaseous mix turewhich have dipole moments.

It should be understood that liquids as well as gases may be analyzed byany of the systems comprising the instant invention, since the normalvapor pressure of many liquids is ample for providing the desiredcontrol of coupling between the input and output wave propagationelements of the system.

Among the objects of the invention are to provide unique methods of andmeans for analyzing gaseous mixtures. A second object of the inventionis to provide improved methods of and means for measuring the dipolemoments of gases or vapors. Another object is to provide improvedmethods of and means for measuring dipole moments of continuouslycirculating gases or vapors. A further object is to provide improvedmethods of and means for controlling continuous gas processes as afunction of the dipole moments of predetermined gaseous or vaporcomponents of the vapors, and the magnitude of an electrostatic fieldthrough which said microwaves are propagated and to which said gases orvapors are subjected.

A further object of the invention is to provide an improved method ofand means for analyzing the composition of gases or vapors having dipolemoments by utilizing a plurality of perpendicularly disposed waveguidesor cavity resonators wherein'the coupling between said waveguides orresonators is controllable as a combined function of the frequency ofmicrowaves propagated therethrough, the dipole moments of gases orvapors enclosed within said system and the magnitude of an electrostaticfield to which said gases or vapors and said microwave propagation aresubjected. A still further object of the invention is to provide animproved method of and means for analyzing the composition of gases orvapors having dipole moments wherein said electrostatic field is variedin accordance with modulation signals, and wherein an oscillographicindicator provides visual indications of the relative dipole moments andrelative quantities of gases or vapors having such dipole moments.

The invention will be described in greater detail by reference to theaccompanying drawing of which Figure 1 is a cross-sectional, partiallyschematic diagram of a first embodiment thereof; Figure 2 is across-sectional, partially schematic diagram of a second embodimentthereof; and Figure 3 is a cross-sectional partially schematic diagramof a third embodiment thereof. Similar reference characters are appliedto similar elements throughout the drawing.

Referring to Figure 1 of the drawing, a microwave signal source, notshown, is connected to the input of a first waveguide I having itselectrical I axis E1 in a plane normal to the drawing. The firstwaveguide I is coupled into a propagation wavepath 3 through a microwavepermeable insulating window 5, such for example as a thin layer of mica.The electrical axis E0 of the wavepath 3 is in a horizontal plane. Thewavepath l is coupled through a second microwave permeable insulatingwindow 1 into a second waveguide 9 having its electrical axis E2 in avertical plane. The wide faces comprising, for example, circularmetallic plates II, I3 of the wavepath 3 are insulated from each otherby an insulating spacer I5 such as polystyrene. Gases or vapors havingdipole moments are confined within or circulated through the wavepath 3.A source of unidirectional voltage, such for example as a battery ll,having a voltage divider l9 and a voltmeter 2| shunted therewith isconnected between the wavepath wide faces II, II, to apply thereto aunidirectional potential to establish an adjustable electrostatic fieldin the plane E0. Each of the two Waveguides operates in the TElO mode.

The fundamental equation for describing the precession of a moleculeabout the lines of electric force between conductors II and i3 is E psin 0E p cos 0=%% (0 sin 0 (l) stant, and is an integer provided byqialgntum mechanics. E1 has a frequency v=uol and and the dipoles arealways perpendicular to E and all rotate in synchronism with said ileld,thus.-

providing transmission of microwave energy from the first waveguide I tothe second waveguide 9. Then n p J and E0 may be swept through the valuefor resonance at a low frequency rate such as 60 cycles, and theresonance curve may be observed on an oscilloscope, thus providing aconvenient measure of the dipole moment of the gas or vapor and a usefulmethod of gas or vapor analysis.

The theory of rotating dipoles in an electrical field was developed byMannebeck in Phys. Zeitschrift 28, 72 (1927) and a satisfactory summarythereof is provided in Electric and Magnetic susceptibilities byVanVleck (Oxford 1932) pp. 147-155.

For symmetrical top molecules the expression provided heretofore, namelyEop=1hv, where U=w0/21r is not correct, but instead three quantumnumbers (1', m, A) must be employed. The correct expression for thesymmetrical top molecule is Eop=2hp (4) The latter equation provides thecorrect relationship between E0, the electric field strength in esu percm.; I the dipole moment; h, the Planck's constant, and v, the operatingfrequency.

If E0 is expressed in volts per cm, Po is expressed in Debye units (aDebye unit=10- esu units of charge x cm.), and o is expressed inmegacycles, then v Eo= '%v volts/cm. (5) since Plancks constant is 655xergs per second.

For methyl chloride, p=1.85, while for emmonia (NI-I3) p=1.5, and formethyl bromide p=1.3 Debye units. Accordingly, if a microwave frequencyof 1000 me. or a wavelength of cm. is employed, Eo=2100 volts per cm.for methyl chloride (CHaCl) but 3020 volts per cm. for methyl bromide(CI-IaBr). Thus if an operating microwave wavelength of the order of 30cm. is employed, transmission from the first to the second waveguide maybe obtained at discrete and widely differing values of E0, depending onthe gas used for coupling.

If the system is operated at a wavelength of 3 cm. instead of 30 cm.,the field strength required for transmission would be 21,000 and 30,200volts per cm., respectively. Such extremely high voltages would giverise to corona discharges unless the system were operated at gaspressures considerably above 1 atmosphere. To avoid the high voltagegradients required for operation at 3 cm., and simultaneously to obtaina narrow voltage nator technique is indicated.

be emphasized that 30 cm. waveguides may be emgradient range over whichthe transmission effect may be observed, operation at wavelengths of theorder of 30 cm. is preferable whereby the gas pressure may be reduced tovalues as low as 10" mm. of mercury for satisfactory operation.

However, a pressure of 1 mm. of the gas under observation may be used toobtain enhanced effects. To prevent corona discharge and simultaneouslyto avoid pressure broadening of the spectral line, a non-polar gas suchas argon or nitrogen is added until the total pressure is such thatthere is no voltage break down at 2000 to 3000 volts per centimeter. Thetotal pressure should be of the order of 10 cm. of mercury or less.

However, since waveguides become cumbersome for transmission ofmicrowaves having wavelengths of the order of 30 cm., a cavity reso-Moreover, it should ployed, but that in order to maintain reasonablyuniform field conformation, wire grills, arranged perpendicularly toeach other, should be placed across the openings between the waveguides.

Referring to Figure 2, a convenient form of cavity resonator systemaccording to the invention comprises a pair of telescoped rectangularcavity resonators A and B having a common portion 3| disposed betweentwo parallel disposed wire screens 33, 35, or slotted walls, havingperpendicularly disposed screen apertures. The two resonators A and Bare separated by an insulated gasket 31,,whereby the slotted screens 33,35 may be maintained at an adjustable unidirectional potential by meansof the battery I! and voltage divider I 9. A microwave source, notshown, is coupled into the first cavity resonator A by means of an inputcoaxial line 39 terminated in an input coupling loop 4| disposed in aplane normal to the drawing. Similarly the second cavity resonator B iscoupled by means of an output coupling loop 43 in a plane parallel withthe drawing, and through an output coaxial line 45 to a microwavedetector 41 including an indicator 49.

Due to the perpendicularly disposed wire screens 33 and 35, there willbe substantially no microwave coupling between the cavity resonators Aand B unless the dipole moments of gases or vapors circulated throughthe two cavity resonators, the applied microwave frequency, and thestrength of the electrostatic field established between the screens 33and 35 are so related that the electric field is rotated through anangle of in the coupling space 3i between the wire screens. The gas tobe tested may be confined within the two cavity resonators or it may becirculated continuously therethrough from a gas or vapor conduit system,the inlet portion 5| and outlet portion 53 only being shown. The systemis operative in the same manner as that described heretofore byreference to the device in Figure Lsince the electric vectors of thecavity resonators A and B are in perpendicular relation due to theperpendicular orientation of the apertures of the wire screens 33 and35. The coupling between the cavity resonators is entirely controlled bythe synchronous rotation of the gaseous molecules in the region 3|common to both cavity resonators.

A continuous and direct indicating system for measuring the presence andquantities of gases having dipole moments in a gaseous mixture is shownin Figure 3 wherein a microwave source 61' is coupled through the inputcoaxial line 39 and terminated in an input coupling loop ll arranged ina plane normal to the drawing. The input coupling loop' BI is coupledinto the first cavity resonator A which intersects the second cavityresonator B and has a common coupling space 3|, as described heretoforeby reference to Figure 2. Instead of wire screens 33 and 35 comprisingconductors arranged in perpendicular relation, slotted walls 33 and 35'having perpendicularly disposed slots, may be employed. The outputcoupling (loop 43 and output coaxial line 45 are coupled from the secondcavity resonator B to a microwave receiver 63, the demodulated output ofwhich is coupledto the vertical deflecting elements 65 of a cathode rayoscilloscope 61. In order that the system may be swept through apredetermined dipole moment range for simultaneously indicating thepresence of a number of different gases having different electric axesfor analyzing the composition of gases or vapors having dipole moments,comprising applying an electric field to said gases or vapors in anintermediate wavepath disposed between and coupling together saiddevices, varying the strength of said field to control said wave by, orsynchronized with, the modulated signal I .dash linecurve 8|, to spreada. desired portion coupling between said devices as a combined functionof said field strength and the dipole moments of said gases, andindicating the characteristics of said composition as a function of saiddipole moments and of said field strength in said intermediate wavepath.

2. The method of utilizing a pair of wave propagation devices havingperpendicularly disposed electric axes for analyzing the composition ofgases or vapors having dipole moments, comprising applying an electricfield to said gases or vapors in an intermediate wavepath disposedbetween and coupling together said devices, Varying the strength of saidfield to control said wave coupling between said devices as a combinedfunction of said field strength and the dipole moments of said gases,and indicating the characteristics of said composition as a, combinedfunction of said dipole moments, the frequency of said wave propagation,and of said field strength in said intermediate wavepath.

.3. The method of utilizing a pair of wave propagation devices havingperpendicularly disposed electric axes for measuring the dipole momentsof gases or vapors, comprising applying an electric field to said gasesor vapors in an intermeof the timingv scale on the horizontal axis ofthe oscilloscope. Various methods and systems for providing suchmodified sawtooth timing signals are well known in the oscillographicart.

In operation, adjustment of the tap 13 on the high voltage source H(which should be of the order of 2000 to 3000 volts) determines themedian value of the dipole moment range to be indicated, and themagnitudes of the modulation signals superimposed upon theunidirectional potential determine the upper and lower limits of thedipole moment scale. The presence of gases or vapors having dipolemoments in the gaseous mixture circulated through or confined within thecavity resonators A and B thus provide v'ertical deflection of theoscilloscope cathode rayat one ormore points on the horizontal scale.The magnitude of the vertical deflection is characteristic of thequantity of gas present'in the mixture for gases or vapors of eachdipole moment value. The horizontal scale may be calibrated in values ofdipole moment or in terms of, known gaseous-or vapor components. Asexplained heretofore, the dipole moment scale also may be shifted byselection of a diiferent applied microwave frequency. The ,modulationsignal source 59 may have any desired low frequency providing asufficiently high rate of horizontal scanning for satisfactoryobservation.

Thus the invention disclosed and claimed herein comprises .severalsystems for measuring and wave propagation between a pair of waveguidesor cavity resonators in which the electrical fields are, normallyperpendicular. I claim as my invention: 1. The method of utilizing apair of wave propadiate wavepath disposed between and coupling togethersaid devices, varying the strength of said field to control said wavecoupling between said devices as a combinedfunction of said fieldstrength and the dipole moments of said gases, and indicating saiddipole moments as a function of said field strength in said intermediatewavepath.

4. Apparatus for analyzing the composition of gasesor vapors havingdipole moments including a, pair of wave propagation devices havingperpendicularly disposed electric axes, an intermediate wave propagationpath disposed between and coupling together said devices, means forapplying an electric field to said intermediate wavepath, means forvarying the strength of said field to control said wave coupling betweensaid devices as a combined function of said field strength and saiddipole moments, and means coupled to one of said devices for indicatingthecharacteristics of said composition as a. function of the magnitudeofwave propagation between said devices and of saidfieldstrength in saidintermediate wavepath.

5. Apparatus for measuring the dipole moments of gases or vaporsincluding a, pair of wave an electric field to said intermediatewavepath,

means for varying the strength of said field to control said wavecoupling between said devices as a combined function of said fieldstrength and said dipole moments, and means coupled to one of saiddevices for indicating said dipole moments as a function of said fieldstrength in said intermediate wavepath.

6. Apparatus for analyzing the composition of gases or vapors havingdipole moments including a. pair of wave propagation devices havingperpendicularly disposed electric axes, a source gation devices havingperpendicularly disposed of microwave i als coupled intov one of said 9devices, a microwave signal output circuit coupled ,to the other of saiddevices, an intermediate wave propagation path disposed between andcoupling together said devices, means for applying an electric field tosaid intermediate posedelectric axes, an intermediate wavepath disposedbetween and coupling together said de-\ vices, means for introducingsaid gases or vapors into said intermediate wavepath, means for ap-'plying an electric field to said intermediate wavepath, means forvarying the strength of said field to control said wave,coupling betweensaid pair of waveguides as a combined function of said field strengthand said dipole moments, and

means coupled into one of said waveguides for indicating thecharacteristics of said composition as a function of said wave couplingbetween said pair of waveguides and of field strength in saidintermediate wavepath.

8. Apparatus for analyzing the composition of gases or vapors havingdipole moments including a pair of microwave cavity resonators having ofgases or vapors having dipole moments includperpendicularly disposedelectric axes, a source of microwave signals coupled into one of saidresonators, a microwave signal output circuit coupled to the other ofsaid resonators, an intermediate wave propagation path disposed betweenand coupling together said resonators, means for applying an electricfield to said intermediate wavepath, means for varying the strength ofsaid field to control said wave coupling between said resonators as acombined function of said field strength and said dipole moments, andmeans coupled to said output circuit for indicating the characteristicsof said composition as a function of the magnitudes of said outputsignals and of said fleld strength in said intermediate wavepath.

9. Apparatus for analyzing the composition of gases or vapors havingdipole moments including an enclosed conductive gas or vapor chamberhaving a pair of conductive apertured elements disposed transverselytherein, the apertures in said elements being perpendicularly disposedto provide a pair of intersecting microwave cavity resonators havingperpendicularly disposed electric axes, a source of microwave signalscoupled into one of said resonators, a microwave signal output circuitcoupled to the other of said resonators, the space between said screenelements common to said resonators comprising an intermediate wavepropagation path coupling together said resonators, a source of voltage,means for applying said voltage to said elements to provide an electricfield'in said space, means for varying the strength of said fleld tocontrol said wave coupling between said resonators as a combinedfunction of the strength of said field and said dipole moments, andmeans coupled to said output circuit for indicating the characteristicsof said composition as a function of the magnitudes of said outputsignals and of said field strength in said intermediate wavepath.

10. Apparatus for analyzing the composition having a pair of conductiveapertured elements disposed transversely therein, the apertures in saidelements being perpendicularly disposed to provide a pair ofintersecting microwave cavity resonators having perpendicularly disposedelectric axes, a source of microwave signals coupled into one of saidresonators, a microwave signal output circuit coupled to the other of.said resonators, the space between said screen. elements common to saidresonators comprising an intermediate wave propagation path couplingtogether said resonators, a source oi. modulation signals, means forapplying said modulation signals to said elements to provide a varyingelectric field in said space to control said wave coupling between saidresonators as a combined function of the strength of said field and saiddipole moments, and means coupled to said output circuit for indicatingthe characteristics of said composition as a function of the magnitudesof said output signals and'ot said field strength in said intermediatewavepath.

' 11. Apparatus for analyzing the composition of gases or vapors havingdipole moments including an enclosed conductive gas or vapor chamberhaving a pair ofconductive' apertured elements disposed transverselytherein, the apertures in said elements being perpendicularly disposedto provide a pair of intersecting microwave cavity resonators havingperpendicularly disposed electric axes, a source of microwave signalscoupled into one of said resonators, a microwave signal output circuitcoupled to the nators, the space between said screen elements common tosaid resonators comprising an intermediate wave propagation pathcoupling together said resonators, a source of modulation signals, meansfor applying said modulation signals to said elements to provide avarying electric field in said space to control said wave coupling'between said resonators as a combined function of the strength of saidfield and said dipole moments, and an oscillograph coupled to saidoutput circuit and to said modulation signal source for indicating thecharacteristics of said composition as a function of the magnitudes ofsaid output signals and of said field strength in said intermediatewavepath.

12. Apparatus according to claim 10 including a source of voltage, meansfor applying said voltage to bias said apertured elements, and

, means for adjusting said bias voltage to control the effective rangeof said indications.

13, Apparatus for analyzing the composition of gases or vapors havingdipole moments including an enclosed conductive gas or' vapor chamberhaving a. pair of conductive apertured elements disposed transverselytherein, the apertures in said elements being perpendicularly disposedto providea pair of intersecting microwave cavity resonators havingperpendicularly disposed electric axes, a source of microwave signalscoupled into one of said resonators, a microwave signal output circuitcoupled to the other of said resonators, the space between said screenelements common to said resonators comother of said reso-.

lation signal source for indicating the charac? teristics of saidcomposition as a function of the magnitudes of said output signals andof said field strength in said intermediate wavepath.

14. The method of utilizing gases or vapors having dipole moments forcontrolling microwave coupling between a pair of microwave propagationdevices having perpendicularly disposed electric axes comprisingapplying an electric field to said gases or vapors in an intermediatewavepath disposed between and coupling together said devices, andvarying the strength of said field to control said wave coupling betweensaid devices as a combined function of said field strength and thedipole moments of said gases.

15. Apparatus for coupling together a pair of 0 2,423,383

microwave propagation devices having perpenl2 dicularly disposedelectric axes comprising an intermediate wave propagation path disposedbetween and coupling together said devices, a microwave energyabsorptive gas or vapor having a dipole moment disposed within saidintermediate wavepath, means for applying an electric field to saidintermediate wavepath, and means for varying the strength of said fieldto control 1 said wave coupling between said devices as a combinedfunction of said field strength and said dipole moment.

WILLIAM D. HERSHIBERGER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Hershberger July 1, 1947 Number

